The continuing development of portable electrically powered devices such as tape recorders and playback machines, radio transmitters and receivers, and the like, create a continuing demand for the development of reliable, long service life cells or batteries for their operations. Recently developed electrochemical cell systems that will provide a long service life utilize highly reactive anode materials such as lithium, sodium and the like, in conjunction with high energy density non-aqueous liquid cathode materials and a suitable salt.
It has recently been disclosed in the literature that certain materials are capable of acting both as an electrolyte carrier, i.e., as solvent for the electrolyte salt, and as the active cathode for a nonaqueous electrochemical cell. British Pat. No. 1,409,307 discloses a nonaqueous electrochemical cell comprising an anode, a cathode collector and a cathode-electrolyte, said cathode-electrolyte comprising a solution of an ionically conductive solute dissolved in an active cathode depolarizer wherein said active cathode depolarizer comprises a liquid oxyhalide of an element of Group V or Group VI of the Periodic Table. The "Periodic Table" is the Periodic Table of Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 48th Edition, The Chemical Rubber Co., Cleveland Ohio, 1967-1968. For example, such nonaqueous cathode materials would include sulfuryl chloride, thionyl chloride, phosphorus oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide and selenium oxychloride.
Another class of liquid cathode materials would be the halides of an element of Group IV to Group VI of the Periodic Table. For example such nonaqueous cathode material would include sulfur monochloride, sulfur monobromide, selenium tetrafluoride, selenium monobromide, thiophosphoryl chloride, thiophosphoryl bromide, vanadium pentafluoride, lead tetrachloride, titanium tetrachloride, disulfur decafluoride, tin bromide trichloride, tin dibromide dichloride and tin tribromide chloride.
However, one possible disadvantage to the use of a liquid cathode such as thionyl chloride is that if it is not uniformly distributed along the surface of an anode, such as lithium, via a separator, then non-uniform anode consumption could occur and may result in low voltage output, particularly at high discharge rates, and longer voltage delays after storage. In addition, non-uniform distribution of the liquid cathode which could occur from non-uniform liquid cathode wetting of the separator, could cause non-uniform anode dissolution. This non-uniform anode dissolution causes high points and plateaus to form on the anode which may possibly result in localized heating during charging (abuse condition) and might lead to the possibility of anode melting at these discrete points. This could lead to a violent venting of the cell or even to cell disassembly. It is believed that the non-uniform wetting of the separator by the liquid cathode is responsible for decreasing the capacity output of the cell.
It is therefore an object of this invention to provide a cell employing a liquid cathode with a separator that can be uniformly wetted by the liquid cathode and thereby result in an improved discharge performance of the cell, particularly on high rate discharge, and improved safety characteristics of the cell.
Another object of the present invention is to provide a separator for liquid cathode cells that can uniformly absorb large amounts of the liquid cathode and at a fast rate.
Another object of the present invention is to provide a separator for a lithium/oxyhalide cell that can uniformly absorb large amounts of the oxyhalide which will result in improvement in the discharge performance of the cell on high rate discharge and improve the safety characteristics of the cell when exposed to abusive conditions such as charging.
The foregoing additional objects will become more fully apparent from the description hereinafter provided.